As Andre says, A guest with 2vCPU and 2cores will use 4 logical CPU on the host. as will a guest with 1vCPU and 4 cores, or a Guest with 4vCPU.
all that has changed is how it is presented to the Guest OS. personally if I am playing with Cores I tend to keep vCPU count as low as possible, this has the added advantage of lowering Socket based licensing costs
